Stable tetracycline solutions



United States Patent 3,389,174 STABLE TETRACYCLINE SOLUTIONS Robert Arnold Nash, Spring Valley, and Bruce Edwin Haeger, Pomona, N.Y., assignors to American Cyanamid Company, Stamford, Conn., a corporation of Maine No Drawing. Original application Oct. 4, 1962, Ser. No. 228,261, new Patent No. 3,219,529, dated Nov. 3, 1965. Divided and this application May 10, 1965, Ser. No.

6 Claims. (Cl. 260-559) ABSTRACT OF THE DISCLOSURE Stable solutions of neutral tetracycline antibiotics in substantially completely esterified lower alkyl esters of lower aliphatic polyhydroxy alcohols and lower alipha tic acids. Triacetin is the preferred glycerol ester and has been found useful in the preparation of stable solutions of tetracycline antibiotics useful for topical or other therapeutic uses.

This application is a division of our copending appli cation Ser. No. 228,261, filed Oct. 4, 1962, now US. Patent No. 3,219,529.

This invention relates to stable antibiotic solutions of the tetracycline group. As used in the specification and claims the term antibiotic solution means a solution containing substantial amounts of antibiotic. Compositions containing small traces of antibiotic are not included.

In the past there has been a demand for solutions of tetracycline antibiotics which would be stable and which could be used for topical or other therapeutic uses. For the most part the solutions have been prepared by forming ,metal complexes with the tetracyclines. Stability has been achieved but in a number of cases the presence of metal ion complexes are not always desirable, and while they have been practically useful, there is still a need for stable, relatively non-toxic solutions of neutral tetracycline antibiotics. It is with the solution of this problem and with stable solutions that the present invention deals. It should be understood that in the present invention we are concerned with so called neutral tetracyclines, that is to say the amphoteric tetracyclines themselves, and not their salts with various acids or bases.

The requirements for satisfactory tetracycline antibiotic solutions require stability on storage at room temperatures, lack of toxicity and retention of the antibiotic activity. Reasonable compatibility with water is also a desirable characteristic as sometimes the solutions are utilized in aqueous media.

Basically, the present invention is concerned with stable solutions of neutral tetracycline antibiotics in esters of lower polyhydric alcohols with lower alkyl fatty acids. These esters should in general have no free hydroxyl groups. Among the best are the glycerol esters, such as triacetin. The corresponding triester of propionic acid can, of course, also be used, but as it shows no advantages over triacetin and is more expensive triacetin is the preferred member of the ester group.

The invention will be described in greater detail in conjunction with the following specific examples. In each case the solution is prepared with thorough stirring. It should be noted that the tetracycline antibiotic weights are in the neutral form, rather than the customary basis as the hydrochlon'des. The pH values in the samples were measured potentiometrically using glass and saturated calomel electrodes.

Example 1 2.37 grams of neutral tetracycline are dissolved in 50 Example 2 2.34 grams of demethyltetracycline are dissolved in ml. of triacetin. The solution shows a bulk pH of 6.6 which decreases to 4.8 on 1:1 dilution with water.

Example 3 5.57 grams of chlortetracycline are dissolved in 100 ml. of triacetin producing a stable solution.

Example 4 Example 1 is repeated, replacing the 50 ml. of triacetin with the same amount of the triester of glycerol and propionic acid. A stable solution results but exhibits the same characteristics as with triacetin, namely there is a slight precipitation on prolonged storage.

Example 5 Example 1 is repeated, replacing the triacetin with an equal amount of ethyleneglycol diacetate. A stable solution results.

Example 6 The procedure of Example 5 is repeated, replacing the ethyleneglycol acetate with the corresponding dipropionate. A stable solution results.

Example 7 The procedure of Example 5 is repeated, replacing the ethylene glycol diacetate with an equal amount of butylene glycol diacetate. A stable solution results.

Example 8 The stability of the solutions of the present invention were tested against other typical organic solvents in two ways. First, by an accelerated test, autoclaving at 121 C., and secondly, at a lower temperature for a longer period of storage. In every case the antibiotic was tetracycline and the concentration 50 mg./ml. Table 1 shows the stability after autoclaving.

TABLE 1AU'IOCLAVE STABILITY OF NEUTRAL TETRA- (50 MGJML. AS TC.HCl) IN VARIOUS SOLVENTS Microbiological activity (percent of th y) Solvent cor 30 min. 60 min. min.

Diethyl nicotinamide 66 51 27 Dimethyl acetarnide. 43 2'8 20 Dimethyl lactarnide 16 17 17 1,3-dioxo1ane 46 39 32 Ethanol (abs) 36 12 2 Isopropylidene glyc 67 58 42 Monoacotin 10 10 10 Polyethylene glycol 400.. 58 3? 5 Propylene glycol 5 5 5 Triacetin 83 82 76 It will be noted that even at two-hours autoclaving the solution of triacetin retained at least two-thirds of its antibiotic activity, whereas the best that any other solvent did, isopropylidene glycol was less than half. It should also be noted that the presence of a hydroxy group as shown by monoacetin completely destroys stability.

Example 9 Tests were made at room temperature and 42 C. for extended periods of time. The results of these tests are shown in Table 2. As in the case of the preceding tests, the solution was of tetracycline in a concentration of 50 mg./m1.

tion is markedly decreased by the presence of such materials as Water, bases, for example, triethanolamine, acids such as ascorbic acid, lactic acid, acetic acid, sulfuric acid,

TABLE 2.STABILITY OF NEUTRAL TETRACYCLINE (50 MGJML. AS TC.

HCl) IN VARIOUS SOLVENTS AT LOW TEMPERATURES Microbiological Activity (Percent of Theory) It will be noted that even at a shorter total length of time diethyl nicotinarnide and isopropylidene glycol showed marked losses of activity as compared to the solution of triacetin.

Example Tests were also made using other neutral tetracycline antibiotics in the solvent of the present invention. The results of this stability at room temperature for extended periods of storage are shown in Table 3.

TABLE 3.STABLE SOLUTONS OF OTHER NEUTRAL TETRACYCLINE ANTIBIOTICS AT THERAPEUTIC LEVELS Microbiological Activity,

C0nvcn., Percent 0: Theory System Ing./ml. (room temperature) 2 mom. 1 year CTC/Triacetin. 25 98 OTC I'Iriacctin- 10 J8 DMC'lC/Triace 10 101 DMTC/Triaeetin 25 98 90 etc. Also certain solid adjuvants such as nicotinamide, isosorbide itself, caprolactam, should not be present. It should be noted that while the presence of water decreases the stability on long standing this does not mean that the products of the present invention may not be used when diluted with water. In fact this is often done but once diluted they will not retain their long-term stability. In addition to the excellent physical and chemical stability of the solutions in triacetin and the like, the ready dilution with water exhibited by these products is an advantage for many uses.

We claim:

1. Stable solutions of neutral tetracycline antibiotics in triacetin.

2. Solutions according to claim 1 in which the tetracycline antibiotic is tetracycline.

3. Solutions according to claim 1 in which the antibiotic is oxytetracycline.

4. Solutions according to claim biotic is demethyltetracyciine.

5. Solutions according to claim biotic is demethylchlortetracycline.

6. Solutions according to claim biotic is chlortetracycline.

1 in which the anti- 1 in which the anti- 1 in which the anti- No references cited.

NICHOLAS S. RIZZO, Primary Examiner. 

